3 ms·

EPIRB is a fantastic technology, saving thousands of people at sea every year. A modern beacon will do a quarter second burst of digital information at 406 MHz

by chx 9y ago

EPIRB is a fantastic technology, saving thousands of people at sea every year. A modern beacon will do a quarter second burst of digital information at 406 MHz at five watts (which is a helluva lot) then becomes silent for about 50 seconds. Today it is precise enough that only about two square kilometres needs to be searched. Fun fact: the 50 seconds is randomized so that two beacons don't become sync'd. A real lot of thought went into creating the protocol. As for the devices, the author was only half kidding about them surviving a nuclear war. Once deployed it's less tough but their brackets (which most autodeploy from if it gets four metres deep) definitely survives some real bad stuff although I can't find hard data on how they are tested.

colanderman 9y ago
I know I'm nitpicking, but... 5 watts isn't a "helluva lot". Consumer WiFi can transmit up to 1 watt. Entry-level ham radio operators can transmit up to 5 watts. If you put a 5 watt transmitter at 406 MHz inside your house, it's possible the signal might not even be strong enough to be received outside, depending on what the walls are made of. Now, consumer radio/television broadcasts... those run in the 10-100 kilowatt range. That's a "helluva lot".
- burntrelish1273 9y ago
  I worked at Trimble Nav in the radio group. 5W for a consumer device is on the high end. UHF base stations often do around 25W-50W+ for wide-area coverage on top of a tower. If you did like a coworker did with a YAGI antenna and accidentally place a base-station onto high-power mode, nearby flesh (<10cm) will receive a significant radio burn.
  - mcguire 9y ago
    Speaking as a software guy, I love stories about hardware. :-)
- Aloha 9y ago
  Unless you're living in a reinforce concrete bunker with no windows - like a bomb shelter - 5w is good for about a mile or so - considering that the beacons go skyward, its worth even more.
- jlgaddis 9y ago
  From right here, in my office in my home in the middle of a town, I can easily communicate via a 440 MHz repeater about eight miles away with a handheld radio (with a little stubby antenna on it) that is putting out about one watt. You need to get much higher up in the spectrum before you have to worry about your signal not passing through walls. To illustrate, mobile phones typically operate in the 800-900 and/or 1800-1900 MHz range and typically put out ~0.6 watts. Most people have no problems whatsoever using their cell phones from inside their homes. 5 watts on 406 MHz out in the middle of an empty ocean is certainly more than enough to be picked up by a satellite passing overhead. Last, "entry-level ham radio operators" are permitted 1500 watts (on the frequency bands we're discussing; the limit is a very reasonable 100 watts on the lower/HF bands). (If you insist on "nitpicking", you should at least make sure you're accurate.)

by chx 9y ago

colanderman 9y ago

I know I'm nitpicking, but... 5 watts isn't a "helluva lot". Consumer WiFi can transmit up to 1 watt. Entry-level ham radio operators can transmit up to 5 watts. If you put a 5 watt transmitter at 406 MHz inside your house, it's possible the signal might not even be strong enough to be received outside, depending on what the walls are made of. Now, consumer radio/television broadcasts... those run in the 10-100 kilowatt range. That's a "helluva lot".

burntrelish1273 9y ago
I worked at Trimble Nav in the radio group. 5W for a consumer device is on the high end. UHF base stations often do around 25W-50W+ for wide-area coverage on top of a tower. If you did like a coworker did with a YAGI antenna and accidentally place a base-station onto high-power mode, nearby flesh (<10cm) will receive a significant radio burn.
- mcguire 9y ago
  Speaking as a software guy, I love stories about hardware. :-)
Aloha 9y ago
Unless you're living in a reinforce concrete bunker with no windows - like a bomb shelter - 5w is good for about a mile or so - considering that the beacons go skyward, its worth even more.
jlgaddis 9y ago
From right here, in my office in my home in the middle of a town, I can easily communicate via a 440 MHz repeater about eight miles away with a handheld radio (with a little stubby antenna on it) that is putting out about one watt. You need to get much higher up in the spectrum before you have to worry about your signal not passing through walls. To illustrate, mobile phones typically operate in the 800-900 and/or 1800-1900 MHz range and typically put out ~0.6 watts. Most people have no problems whatsoever using their cell phones from inside their homes. 5 watts on 406 MHz out in the middle of an empty ocean is certainly more than enough to be picked up by a satellite passing overhead. Last, "entry-level ham radio operators" are permitted 1500 watts (on the frequency bands we're discussing; the limit is a very reasonable 100 watts on the lower/HF bands). (If you insist on "nitpicking", you should at least make sure you're accurate.)